Scalable Co-MOF thin films for OER: Achieving low overpotential and enhanced catalytic activity via surface reconstruction

The cost reduction remains a critical challenge for the green hydrogen economy, necessitating the replacement of expensive RuO₂ and IrO₂ catalysts for the oxygen evolution reaction (OER). Metal-organic frameworks (MOFs), with their high surface area, porosity, and tunable properties, emerge as promising alternatives for efficient and cost-effective OER. This study uses the Reaction-Diffusion method with varying metal concentrations to explore the cost-effective and binder-free synthesis of Co-MOF thin films on a stainless steel substrate. The optimised CoM-2 thin film demonstrating an overpotential of 275 mV at 10 mA cm⁻², a Tafel slope of 76 mV.dec⁻¹ and an impressive ECSA of 251 cm² for OER. The FESEM study revealed its unique jasmine flower-like clusters grown a top vertically well-aligned rod-like surface morphology, while XPS confirmed the presence of high pyridine-nitrogen content and moderate content of Co–N, which enhances its catalytic efficiency. The binder-free synthesis approach further contributes to the exceptional catalytic activity of CoM-2. In the prototype water electrolysis setup, the CoM-2 thin film achieved a hydrogen evolution rate of 1244 mL per hour and demonstrated good stability with increasing rate of production over 100 h of continuous operation. This enhancement in activity is attributed to surface reconstruction in the alkaline medium, where surface-exposed ligands attached to cobalt were replaced with oxyhydroxide groups and increased the number of active sites for OER. These findings highlight Co-MOF thin film as an efficient, economical, scalable electrocatalyst for OER in sustainable energy applications.